The present invention relates to the preparation and use of aqueous alkaline solutions for displacing a relatively acidic oil within a subterranean reservoir to recover the oil or at least displace it within the reservoir. More particularly, the invention relates to proportioning the components of such a solution to reduce the tendency for the solution to dissolve silica without significantly reducing the oil displacing efficiency of the solution.
Numerous processes involving injections of oil-displacing aqueous alkaline solutions into subterranean reservoirs are described in U.S. patents. For example, U.S. Pat. No. 3,777,817 describes a pretreatment injection of a solution of sacrificial material, such as sodium hydroxide or sodium silicate, into a reservoir in which such "sacrificial materials" do not themselves have any appreciable effect on the oil recovery efficiency of waterflooding operations" (Col. 3, lines 37-39). U.S. Pat. No. 3,805,893 describes injecting alternating slugs of aqueous alkali silicate solutions which are capable of saponifying the reservoir oil and slugs of reactants which are capable of precipitating or gelling the silicate solutions. U.S. Pat. No. 3,871,452 describes a process like that of the 3,805,893 patent in which an aqueous sodium hydroxide solution is injected ahead of the alternating slugs. U.S. Pat. No. 3,871,453 describes a process like that of the 3,805,893 patent in which a slug of crude oil emulsified with an aqueous silicate solution is injected ahead of the alternating slugs. U.S. Pat. No. 3,920,074 describes a process of recovering oil by injecting the slug of aqueous alkali metal silicate ahead of flood water in order to displace oil which is restricting the rate at which the flood water can be injected. U.S. Pat. No. 3,927,716 describes recovering oil by injecting an aqueous alkaline solution having a specified range of pH and of monovalent salt content. U.S. Pat. No. 4,081,029 describes recovering oil by injecting a relatively large slug of aqueous alkali metal silicate solution having a relatively high pH ahead of alternating slugs of the type described in U.S. Pat. No. 3,805,893. U.S. Pat. No. 4,359,093 describes recovering oil by injecting an aqueous solution of alkali metal silicate containing an aminopolycarboxcylic acid chelating agent.
Copending patent application, Ser. No. 411,779 filed Aug. 26, 1982, by D. R. Thigpen, J. B. Lawson and R. C. Nelson describes recovering oil by injecting an aqueous alkaline solution containing a preformed cosurfactant material for increasing the salinity tolerance of the solution and an agent for controlling the rates at which the solution components are propagated through the pores of the reservoir.